Heat-transfer compositions exhibiting improved miscibility with the lubricating oil

ABSTRACT

The use of 1,1,1,2-tetrafluoroethane for increasing the miscibility of 2,3,3,3-tetrafluoropropene with a lubricating oil, and in particular with a polyalkylene glycol oil. Further included are heat-transfer compositions and also equipment and processes using these compositions. Also, a kit including a heat-transfer fluid including 2,3,3,3-tetrafluoropropene and 1,1,1,2-tetrafluoroethane, and a lubricant oil including a polyalkylene glycol, for use in a heat-transfer installation including a vapor compression circuit.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.14/115,542, filed on Nov. 4, 2013, which is a U.S. National Stageapplication of International Application No. PCT/FR2012/050653, filed onMar. 28, 2012, which claims the benefit of French Application No.11.53801, filed on May 4, 2011. The entire contents of each of U.S.application Ser. No. 14/115,542, International Application No.PCT/FR2012/050653, and French Application No. 11.53801 are herebyincorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to heat-transfer compositions based on2,3,3,3-tetrafluoropropene which have improved miscibility withlubricant oil.

TECHNICAL BACKGROUND

Fluids based on fluorocarbon compounds are widely used in vaporcompression heat-transfer systems, especially air-conditioning,heat-pump, refrigeration or freezing devices. The common feature ofthese devices is that they are based on a thermodynamic cycle comprisingvaporization of the fluid at low pressure (in which the fluid absorbsheat); compression of the vaporized fluid up to a high pressure;condensation of the vaporized fluid to liquid at high pressure (in whichthe fluid expels heat); and depressurization of the fluid to completethe cycle.

The choice of a heat-transfer fluid (which may be a pure compound or amixture of compounds) is dictated firstly by the thermodynamicproperties of the fluid, and secondly by additional constraints. Thus, aparticularly important criterion is that of the environmental impact ofthe fluid under consideration. In particular, chlorinated compounds(chlorofluorocarbons and hydrochlorofluorocarbons) have the drawback ofdamaging the ozone layer. Non-chlorinated compounds are therefore nowgenerally preferred, such as hydrofluorocarbons, fluoro ethers andfluoro olefins.

Another environmental constraint is that of the global warming potential(GWP). It is thus essential to develop heat-transfer compositions whichhave a GWP that is as low as possible and good energy performancequalities.

Moreover, to lubricate the moving parts of the compressor(s) of a vaporcompression system, a lubricant oil must be added to the heat-transferfluid. The oil may generally be mineral or synthetic.

The choice of lubricant oil is made as a function of the type ofcompressor, and so as not to react with the heat-transfer fluid itselfor with the other compounds present in the system.

For certain heat-transfer systems (especially small ones), the lubricantoil is generally permitted to circulate throughout the circuit, thepipework being designed such that the oil can flow by gravity to thecompressor. In other heat-transfer systems (especially large ones), anoil separator is provided immediately after the compressor, and also anoil level management device, which ensures return of the oil to thecompressor(s). Even when an oil separator is present, the pipework ofthe system must still be designed such that the oil can return bygravity to the oil separator or to the compressor.

Document WO 2004/037 913 describes compositions based on fluoro olefinsand especially based on tetrafluoropropene or pentafluoropropene.Example 2 reports the miscibility of 1,2,3,3,3-pentafluoropropene(HFO-1225ye) with various lubricant oils, and also that of1,3,3,3-tetrafluoropropene (HFO-1234ze) with various lubricant oils.Example 3 reports the compatibility of HFO-1234ze and of3,3,3-trifluoropropene (HFO-1243zf) with lubricant oils of thepolyalkylene glycol type.

Document WO 2005/042 663 specifically concerns the miscibility ofmixtures of fluoro olefins and of lubricant oils. The examples providedfor these mixtures are essentially the same as those in document WO2004/037 913.

Document WO 2006/094 303 describes a large number of heat-transfercompositions comprising fluoro olefins and additional compounds. Amongthe numerous compositions cited are mixtures based on2,3,3,3-tetrafluoropropene (HFO-1234yf) and 1,1,1,2-tetrafluoroethane(HFC-134a). Moreover, the document generally teaches of combining thelist of the numerous possible refrigerant mixtures with a list oflubricant oils.

When the heat-transfer compound(s) have poor miscibility with thelubricant oil, said oil has a tendency to be trapped in the evaporatorand not return to the compressor, which does not enable correctfunctioning of the system.

In this regard, there is still a need to develop low-GWP heat-transfercompositions (which have good energy performance), in which theheat-transfer compounds show good miscibility with the lubricant oil.

In particular, HFO-1234yf is a heat-transfer compound that isparticularly interesting especially due to its low GWP and its goodenergy performance. On the other hand, its miscibility with certainlubricant oils is imperfect and limits its application. It is thusdesirable to improve the miscibility of compositions based on HFO-1234yfwith the usual lubricant oils.

SUMMARY OF THE INVENTION

The invention relates firstly to a composition comprising2,3,3,3-tetrafluoropropene, 1,1,1,2-tetrafluoroethane and polyalkyleneglycol.

According to one embodiment, 2,3,3,3-tetrafluoropropene,1,1,1,2-tetrafluoroethane and the polyalkylene glycol represent at least95%, preferably at least 99% and more particularly preferably at least99.9% of the composition.

According to one embodiment, the composition comprises from 1% to 99% ofpolyalkylene glycol, preferably from 5% to 50%, more particularlypreferably from 10% to 40% and ideally from 15% to 35%.

According to one embodiment, the mass ratio between2,3,3,3-tetrafluoropropene and 1,1,1,2-tetrafluoroethane is from 1/99 to99/1, preferably from 25/75 to 95/5, more particularly preferably from50/50 to 92/8 and ideally from 55/45 to 92/8.

According to one embodiment, the polyalkylene glycol has a viscosityfrom 1 to 1000 centistokes at 40° C., preferably from 10 to 200centistokes at 40° C., more particularly preferably from 20 to 100centistokes at 40° C. and ideally from 40 to 50 centistokes at 40° C.

According to one embodiment, the composition also comprises: one or moreadditives chosen from heat-transfer compounds, lubricants, stabilizers,surfactants, tracers, fluorescers, odorant agents, solubilizers, andmixtures thereof; preferably one or more additives chosen fromstabilizers, surfactants, tracers, fluorescers, odorant agents andsolubilizers, and mixtures thereof.

The invention also relates to the use of a polyalkylene glycol as alubricant oil in a vapor compression circuit, in combination with aheat-transfer fluid comprising, and preferably consisting of, a mixtureof 2,3,3,3-tetrafluoropropene and 1,1,1,2-tetrafluoroethane.

According to one embodiment, the polyalkylene glycol is used in aproportion of from 1% to 99%, preferably from 5% to 50%, moreparticularly preferably from 10% to 40% and ideally from 15% to 35%,relative to the sum of the polyalkylene glycol and of the heat-transferfluid.

According to one embodiment, the mass ratio between2,3,3,3-tetrafluoropropene and 1,1,1,2-tetrafluoroethane in theheat-transfer fluid is from 1/99 to 99/1, preferably from 25/75 to 95/5,more particularly preferably from 50/50 to 92/8 and ideally from 55/45to 92/8.

According to one embodiment, the mass ratio between2,3,3,3-tetrafluoropropene and 1,1,1,2-tetrafluoroethane in theheat-transfer fluid is from 60/40 to 99.9/0.1, preferably from 68/32 to99.9/0.1, more particularly preferably from 68/32 to 95/5.

According to one embodiment, the polyalkylene glycol has a viscosityfrom 1 to 1000 centistokes at 40° C., preferably from 10 to 200centistokes at 40° C., more particularly preferably from 20 to 100centistokes at 40° C. and ideally from 40 to 50 centistokes at 40° C.

The invention also relates to a heat-transfer installation comprising avapor compression circuit containing a heat-transfer composition whichis a composition as described above.

According to one embodiment, the installation is chosen from mobile orstationary heat-pump heating, air-conditioning, refrigeration, freezingand Rankine-cycle installations, and especially from motor vehicleair-conditioning installations.

The invention also relates to a process for heating or cooling a fluidor a body by means of a vapor compression circuit containing aheat-transfer fluid, said process successively comprising at leastpartial evaporation of the heat-transfer fluid, compression of theheat-transfer fluid, at least partial condensation of the heat-transferfluid and depressurization of the heat-transfer fluid, in which theheat-transfer fluid is combined with a lubricant oil to form aheat-transfer composition, said heat-transfer composition being acomposition as described above.

The invention also relates to a process for reducing the environmentalimpact of a heat-transfer installation comprising a vapor compressioncircuit containing an initial heat-transfer fluid, said processcomprising a step of replacing the initial heat-transfer fluid in thevapor compression circuit with a final heat-transfer fluid, the finalheat-transfer fluid having a lower GWP than the initial heat-transferfluid, in which the final heat-transfer fluid is combined with alubricant oil to form a heat-transfer composition, said heat-transfercomposition being a composition as described above.

The invention also relates to the use of 1,1,1,2-tetrafluoroethane forincreasing the miscibility of 2,3,3,3-tetrafluoropropene with alubricant oil.

According to one embodiment, the lubricant oil is a polyalkylene glycol,and preferably has a viscosity from 1 to 1000 centistokes at 40° C.,more preferably from 10 to 200 centistokes at 40° C., more particularlypreferably from 20 to 100 centistokes at 40° C. and ideally from 40 to50 centistokes at 40° C.

According to one embodiment, the 1,1,1,2-tetrafluoroethane is used in aproportion of from 1% to 99%, preferably from 5% to 75%, moreparticularly preferably from 8% to 50% and ideally from 8% to 45%,relative to the sum of 1,1,1,2-tetrafluoroethane and2,3,3,3-tetrafluoropropene.

The invention also relates to a kit comprising:

-   -   a heat-transfer fluid comprising 2,3,3,3-tetrafluoropropene and        1,1,1,2-tetrafluoroethane, on the one hand;    -   a lubricant oil comprising a polyalkylene glycol, on the other        hand;

for use in a heat-transfer installation comprising a vapor compressioncircuit.

The present invention makes it possible to satisfy the needs felt in theprior art. It more particularly provides low-GWP heat-transfercompositions, which have good energy performance, in which theheat-transfer compounds show good miscibility with the lubricant oil.

In particular, the invention provides heat-transfer compositions basedon HFO-1234yf, which have improved miscibility with certain lubricantoils such as polyalkylene glycols.

This is accomplished by mixing HFO-1234yf with HFC-134a. Thus, thepresent inventors have noted that HFC-134a improves the miscibilityproperties of HFO-1234yf with polyalkylene glycols, beyond that whichmight be expected by a simple extrapolation of the miscibilityproperties of HFO-1234yf, on the one hand, and of HFC-134a, on the otherhand, with the lubricant oil. There is thus a synergistic effect betweenHFO-1234yf and HFC-134a from the point of view of the miscibility withthe lubricant oil.

The oils of polyalkylene glycol type have good lubricant power, a lowflow point, good fluidity at low temperature, and good compatibilitywith the elastomers generally present in a vapor compression circuit.They are moreover relatively less expensive than other lubricant oilsand are oils whose use is currently very widespread in certain fields,and especially in the field of motor vehicle air-conditioning. It istherefore very advantageous to improve the miscibility of HFO-1234yfwith a lubricant oil of the polyalkylene glycol type, so as to be ableto use this heat-transfer compound to a wider extent in combination withthis lubricant oil.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a graph representing the miscibility of various mixtures ofHFO-1234yf and HFC-134a with a polyalkylene glycol ND8 oil. Theproportion of HFC-134a relative to the mixture of HFO-1234yf andHFC-134a is indicated on the x-axis and ranges from 0 to 100%, and thetemperature from which the mixture ceases to be miscible with the oil isindicated on the y-axis (in ° C.). The experimental data are representedby black circles. The abbreviations NM and M denote, respectively, thenon-miscibility zone and the miscibility zone. All the results areobtained with a content of oil ND8 of 17% relative to the sum of thethree compounds HFO-1234yf/HFC-134a and oil ND8. Reference will be madeto the example below for further details.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The invention is now described in greater detail and without limitationin the description that follows.

Unless otherwise mentioned, throughout the application the indicatedproportions of compounds are given as mass percentages.

According to the present patent application, the global warmingpotential (GWP) is defined relative to carbon dioxide and relative to aduration of 100 years, according to the method indicated in “Thescientific assessment of ozone depletion, 2002, a report of the WorldMeteorological Association's Global Ozone Research and MonitoringProject”.

The term “heat-transfer compound” or, respectively, “heat-transferfluid” (or coolant fluid) means a compound or, respectively, a fluidthat is capable of absorbing heat by evaporating at low temperature andlow pressure and of expelling heat by condensing at high temperature andhigh pressure, in a vapor compression circuit. In general, aheat-transfer fluid may comprise one, two, three or more than threeheat-transfer compounds.

The term “heat-transfer composition” means a composition comprising aheat-transfer fluid and optionally one or more additives that are notheat-transfer compounds for the intended application.

The invention is based on the use of two heat-transfer compounds, namelyHFO-1234yf and HFC-134a, and of a lubricant oil, to form a heat-transfercomposition.

The heat-transfer composition may be introduced in unmodified form intoa vapor compression circuit. Alternatively, the heat-transfer fluid(namely HFO-1234yf and HFC-134a), on the one hand, and the lubricantoil, on the other hand, may be introduced separately into the circuit,at the same point or otherwise. The individual heat-transfer compounds(HFO-1234yf and HFC-134a) may also be introduced separately.

The lubricant oil is preferably of the polyalkylene glycol type.

In general, the polyalkylene glycol oil that is suitable for use in thecontext of the invention comprises from 5 to 50 repeated oxyalkyleneunits, each containing from 1 to 5 carbon atoms.

The polyalkylene glycol may be linear or branched. It may be ahomopolymer or a copolymer of 2, 3 or more than 3 groups chosen fromoxyethylene, oxypropylene, oxybutylene and oxypentylene groups andcombinations thereof.

Preferred polyalkylene glycols comprise at least 50% of oxypropylenegroups. For the purposes of the invention, the polyalkylene glycol maycomprise polyalkylene glycols of different formulae as a mixture.

Suitable polyalkylene glycols are described in document U.S. Pat. No.4,971,712. Other suitable polyalkylene glycols are polyalkylene glycolscontaining hydroxyl groups at each end, as described in document U.S.Pat. No. 4,755,316. Other suitable polyalkylene glycols are polyalkyleneglycols having a capped hydroxyl end. The hydroxyl group may be cappedwith an alkyl group containing from 1 to 10 carbon atoms (and optionallycontaining one or more heteroatoms such as nitrogen), or a fluoroalkylgroup containing heteroatoms such as nitrogen, or a fluoroalkyl group asdescribed in document U.S. Pat. No. 4,975,212, or other similar groups.

When the two hydroxyl ends of the polyalkylene glycol are capped, thesame end group or a combination of two different groups may be used.

The end hydroxyl groups may also be capped by forming an ester with acarboxylic acid, as is described in document U.S. Pat. No. 5,008,028.The carboxylic acid may also be fluorinated.

When the two ends of the polyalkylene glycol are capped, one or theother may be capped with an ester, or alternatively one end may becapped with an ester and the other end may be free or may be capped withone of the abovementioned alkyl, heteroalkyl or fluoroalkyl groups.

Examples of commercially available lubricant oils of polyalkylene glycoltype are the Goodwrench oils from General Motors and Mopar-56 fromDaimler-Chrysler. Other suitable oils are manufactured by Dow Chemicaland Denso.

The viscosity of the lubricant oil may be, for example, from 1 to 1000centistokes at 40° C., preferably from 10 to 200 centistokes at 40° C.,more particularly preferably from 20 to 100 centistokes at 40° C. andideally from 40 to 50 centistokes at 40° C.

The viscosity is determined according to the ISO viscosity grades, inaccordance with standard ASTM D2422.

The oil sold by Denso under the name ND8, with a viscosity of 46centistokes, is particularly suitable.

The proportion of lubricant oil that needs to be used in combinationwith the heat-transfer fluid mainly depends on the type of installationconcerned. Specifically, the total amount of lubricant oil in theinstallation depends mainly on the nature of the compressor, whereas thetotal amount of heat-transfer fluid in the installation depends mainlyon the exchangers and on the pipework.

In general, the proportion of lubricant oil in the heat-transfercomposition, or, in other words, relative to the sum of the lubricantoil and of the heat-transfer fluid, is from 1% to 99%, preferably from5% to 50%, for example from 10% to 40% or from 15% to 35%.

According to one particular embodiment, the lubricant oil used consistsof the polyalkylene glycol described above, with the exception of anyother lubricant compound.

According to an alternative embodiment, another lubricant oil is used incombination with the polyalkylene glycol. It may be chosen especiallyfrom oils of mineral origin, silicone oils, paraffins of natural origin,naphthenes, synthetic paraffins, alkylbenzenes, poly-α-olefins, polyolesters and/or polyvinyl ethers. Polyol esters and polyvinyl ethers arepreferred. When another lubricant oil is used in combination with thepolyalkylene glycol it is preferable for the miscibility of theHFO-1234yf and/or of the HFC-134a with this oil to be greater than therespective miscibility of HFO-1234yf and/or of HFC-134a with thepolyalkylene glycol. This is especially the case for at least some ofthe oils of polyol ester or poly vinyl ether type.

The heat-transfer compounds mainly used in the context of the presentinvention are HFO-1234yf and HFC-134a.

However, the heat-transfer compositions according to the invention mayoptionally comprise one or more additional heat-transfer compounds,besides HFO-1234yf and HFC-134a. These additional heat-transfercompounds may be chosen especially from hydrocarbons,hydrofluorocarbons, ethers, hydrofluoro ethers and fluoro olefins.

According to particular embodiments, the heat-transfer fluids accordingto the invention may be ternary compositions (consisting of threeheat-transfer compounds) or quaternary compositions (consisting of fourheat-transfer compounds), in combination with the lubricant oil to formthe heat-transfer compositions according to the invention.

However, binary heat-transfer fluids are preferred.

The term “binary fluid” means either a fluid consisting of a mixture ofHFO-1234yf and HFC-134a; or a fluid consisting essentially of HFO-1234yfand HFC-134a, but which may contain impurities to a proportion of lessthan 1%, preferably less than 0.5%, preferably less than 0.1%,preferably less than 0.05% and preferably less than 0.01%.

According to particular embodiments, the proportion of HFO-1234yf in theheat-transfer fluid may be: from 0.1 to 5%; or from 5 to 10%; or from 10to 15%; or from 15 to 20%; or from 20 to 25%; or from 25 to 30%; or from30 to 35%; or from 35 to 40%; or from 40 to 45%; or from 45 to 50%; orfrom 50 to 55%; or from 55 to 60%; or from 60 to 65%; or from 65 to 70%;or from 70 to 75%; or from 75 to 80%; or from 80 to 85%; or from 85 to90%; or from 90 to 95%; or from 95 to 99.9%.

According to particular embodiments, the proportion of HFC-134a in theheat-transfer fluid may be: from 0.1 to 5%; or from 5 to 10%; or from 10to 15%; or from 15 to 20%; or from 20 to 25%; or from 25 to 30%; or from30 to 35%; or from 35 to 40%; or from 40 to 45%; or from 45 to 50%; orfrom 50 to 55%; or from 55 to 60%; or from 60 to 65%; or from 65 to 70%;or from 70 to 75%; or from 75 to 80%; or from 80 to 85%; or from 85 to90%; or from 90 to 95%; or from 95 to 99.9%.

The values given in the three preceding paragraphs apply to theheat-transfer fluid without lubricant oil, and not to the heat-transfercomposition which comprises the heat-transfer fluid, the lubricant oiland optionally other additives.

The other additives that may be used in the context of the invention maybe chosen especially from stabilizers, surfactants, tracers,fluorescers, odorant agents and solubilizers.

The stabilizer(s), when they are present, preferably represent not morethan 5% by mass in the heat-transfer composition. Among the stabilizers,mention may be made especially of nitromethane, ascorbic acid,terephthalic acid, azoles such as tolutriazole or benzotriazole,phenolic compounds such as tocopherol, hydroquinone,t-butylhydroquinone, 2,6-di-tert-butyl-4-methylphenol, epoxides(optionally fluorinated or perfluorinated alkyl, or alkenyl or aromatic)such as n-butyl glycidyl ether, hexanediol diglycidyl ether, allylglycidyl ether or butylphenyl glycidyl ether, phosphites, phosphonates,thiols and lactones.

As tracers (which can be detected), mention may be made of deuterated ornon-deuterated hydrofluorocarbons, deuterated hydrocarbons,perfluorocarbons, fluoro ethers, bromo compounds, iodo compounds,alcohols, aldehydes, ketones, nitrous oxide and combinations thereof.The tracer is different from the heat-transfer compound(s) of which theheat-transfer fluid is composed.

Examples of solubilizers that may be mentioned include hydrocarbons,dimethyl ether, polyoxyalkylene ethers, amides, ketones, nitriles,chlorocarbons, esters, lactones, aryl ethers, fluoro ethers and1,1,1-trifluoroalkanes. The solubilizer is different from theheat-transfer compound(s) of which the heat-transfer fluid is composed.

Fluorescers that may be mentioned include naphthalimides, perylenes,coumarins, anthracenes, phenanthracenes, xanthenes, thioxanthenes,naphthoxanthenes and fluoresceins, and derivatives and combinationsthereof.

Odorant agents that may be mentioned include alkylacrylates,allylacrylates, acrylic acids, acrylic esters, alkyl ethers, alkylesters, alkynes, aldehydes, thiols, thio ethers, disulfides,allylisothiocyanates, alkanoic acids, amines, norbornenes, norbornenederivatives, cyclohexene, heterocyclic aromatic compounds, ascaridoleand o-methoxy(methyl)phenol, and combinations thereof.

The heat-transfer process according to the invention is based on the useof an installation comprising a vapor compression circuit which containsa heat-transfer composition (namely a heat-transfer fluid and at leastone lubricant oil). The heat-transfer process may be a process forheating or cooling a fluid or a body.

The vapor compression circuit comprises at least one evaporator, acompressor, a condenser and a depressurizer, and also lines fortransporting the fluid between these components. The evaporator and thecondenser comprise a heat exchanger for exchanging heat between theheat-transfer fluid and another fluid or body.

As compressor, use may be made especially of a single-stage ormulti-stage centrifugal compressor or a centrifugal mini-compressor.Rotary, piston or screw compressors may also be used. The compressor maybe driven by an electric motor or by a gas turbine (for example fed withthe exhaust gases of a vehicle, or mobile applications) or by gearing.

The installation may comprise an electricity-generating turbine (Rankinecycle).

The installation may also optionally comprise at least one heat-exchangefluid circuit used for transmitting heat (with or without a change ofstate) between the heat-transfer fluid circuit and the fluid or body tobe heated or cooled.

The installation may also optionally comprise two (or more) vaporcompression circuits, containing identical or different heat-transferfluids. For example, the vapor compression circuits may be coupledtogether.

The vapor compression circuit operates according to a standard vaporcompression cycle. The cycle comprises the change of state of theheat-transfer fluid from a liquid phase (or liquid/vapor two-phasesystem) to a vapor phase at a relatively low pressure, followed bycompression of the fluid in vapor phase up to a relatively highpressure, the change of state (condensation) of the heat-transfer fluidfrom the vapor phase to the liquid phase at a relatively high pressure,and reduction of the pressure to recommence the cycle.

In the case of a cooling process, heat derived from the fluid or bodythat is being cooled (directly or indirectly, via a heat-exchange fluid)is absorbed by the heat-transfer fluid, during the evaporation of thelatter, this taking place at a relatively low temperature relative tothe environment. The cooling processes comprise air-conditioningprocesses (with mobile installations, for example in vehicles, orstationary installations), refrigeration and freezing processes orcryogenic processes.

In the case of a heating process, heat is yielded (directly orindirectly, via a heat-exchange fluid) from the heat-transfer fluid,during the condensation of the latter, to the fluid or body that isbeing heated, this taking place at a relatively high temperaturerelative to the environment. In this case, the installation fortransferring heat is known as a “heat pump”.

It is possible to use any type of heat exchanger for the implementationof the heat-transfer fluids according to the invention, and especiallyco-current heat exchangers or, preferably, counter-current heatexchangers. It is also possible to use micro-channel exchangers.

The invention in particular makes it possible to use cooling processesat moderate temperature, i.e. those in which the temperature of thecooled fluid or body is from −15° C. to 15° C., preferably from −10° C.to 10° C. and more particularly preferably from −5° C. to 5° C. (ideallyabout 0° C.).

The invention also makes it possible to use heating processes atmoderate temperature, i.e. those in which the temperature of the heatedfluid or body is from 30° C. to 80° C., preferably from 35° C. to 55° C.and more particularly preferably from 40° C. to 50° C. (ideally about45° C.).

In the processes of “cooling or heating at moderate temperature”mentioned above, the inlet temperature of the heat-transfer fluid intothe evaporator is preferably from −20° C. to 10° C., especially from−15° C. to 5° C., more particularly preferably from −10° C. to 0° C.,for example about −5° C.; and the condensation start temperature of theheat-transfer fluid in the condenser is preferably from 25° C. to 90°C., especially from 30° C. to 70° C., more particularly preferably from35° C. to 55° C., for example about 50° C. These processes may berefrigeration, air-conditioning or heating processes.

The invention also makes it possible to use cooling processes at lowtemperature, i.e. those in which the temperature of the cooled fluid orbody is from −40° C. to −10° C., preferably from −35° C. to −25° C. andmore particularly preferably from −30° C. to −20° C. (ideally about −25°C.).

In the “low-temperature cooling” processes mentioned above, the inlettemperature of the heat-transfer fluid into the evaporator is preferablyfrom −45° C. to −15° C., especially from −40° C. to −20° C. and moreparticularly preferably from −35° C. to −25° C., for example about −30°C.; and the condensation start temperature of the heat-transfer fluid inthe condenser is preferably from 25° C. to 80° C., especially from 30°C. to 60° C. and more particularly preferably from 35° C. to 55° C., forexample about 40° C.

It should be noted that the addition of HFC-134a to a heat-transferfluid consisting of HFO-1234yf (or comprising HFO-1234yf) improves themiscibility of the heat-transfer fluid with the lubricant oil, i.e.increases the threshold temperature for appearance of thenon-miscibility zone (defined as being the temperature from which thecompounds in the liquid phase form an emulsion), and thus makes itpossible to increase the possibilities of use of the heat-transferfluid, for example by enabling use at a higher condensation temperature.

More generally, the invention enables the replacement of anyheat-transfer fluid in all heat transfer applications, for example inmotor vehicle air-conditioning. For example, the heat-transfer fluidsand heat-transfer compositions according to the invention may serve toreplace:

-   -   1,1,1,2-tetrafluoroethane (R134a);    -   1,1-difluoroethane (R152a);    -   1,1,1,3,3-pentafluoropropane (R245fa);    -   mixtures of pentafluoroethane (R125), 1,1,1,2-tetrafluoroethane        (R134a) and isobutane (R600a), namely R422;    -   chlorodifluoromethane (R22);    -   the mixture of 51.2% chloropentafluoroethane (R115) and 48.8%        chlorodifluoromethane (R22), namely R502;    -   any hydrocarbon;    -   the mixture of 20% difluoromethane (R32), 40% pentafluoroethane        (R125) and 40% 1,1,1,2-tetrafluoroethane (R134a), namely R407A;    -   the mixture of 23% difluoromethane (R32), 25% pentafluoroethane        (R125) and 52% 1,1,1,2-tetrafluoroethane (R134a), namely R407C;    -   the mixture of 30% difluoromethane (R32), 30% pentafluoroethane        (R125) and 40% 1,1,1,2-tetrafluoroethane (R134a), namely R407F;    -   R1234yf (2,3,3,3-tetrafluoropropene);    -   R1234ze (1,3,3,3-tetrafluoropropene).

EXAMPLE

The example that follows illustrates the invention without limiting it.

In this example, the miscibility of HFO-1234yf, HFC-134a and mixturesthereof with a lubricant oil of the type PAG ND8 is studied.

An autoclave is placed in a glass-paneled tank fed with athermostatically maintained bath of water or of glycol-water dependingon the test temperatures, from −30° C. to +80° C.

For each heat-transfer fluid tested (mixture of HFO-1234yf and HFC-134ain given proportions), the heat-transfer fluid is introduced into theautoclave. Next, a first amount of defined lubricant oil is added, andthe mixture is stirred. The temperature in the autoclave is increaseduntil an emulsion is obtained, indicating the non-miscibility of themixture. The mixture is then cooled, an additional amount of oil isadded thereto and this operation is performed iteratively.

This procedure makes it possible to produce, for each givenHFO-1234yf/HFC-134a transfer fluid, a curve for visualization of thenon-miscibility zone of the mixture with the oil PAG, as a function ofthe temperature.

Reciprocally, exploitation of the data makes it possible to determine,for a given lubricant oil concentration, the non-miscibility thresholdtemperature as a function of the proportion of HFC-134a in theHFO-1234yf/HFC-134a mixture. This is shown in FIG. 1, for an amount oflubricant oil of 17%.

When the mixture does not contain any HFC-134a, the emulsion appears ata temperature of 26° C. On the other hand, when the mixture does notcontain any HFO-1234yf, the emulsion appears at a temperature of 69° C.This makes it possible to plot a theoretical dashed line, representingthe expected temperature for the appearance of an emulsion with amixture of HFO-1234yf and of HFC-134a, this being obtained by weightingof the respective miscibility temperatures.

Experimentally, it is noted, however, that the miscibility zone islarger than that theoretically expected. This means that there is asynergistic effect between HFO-1234yf and HFC-134a with regard to themiscibility with the lubricant oil.

A similar result is obtained with an amount of lubricant oil of 30%, forexample, instead of 17%. It is thus observed that the addition of 20%HFC-134a to HFO-1234yf makes it possible to improve the miscibility zoneby about 10 degrees relative to the expected value.

The invention claimed is:
 1. A method comprising replacing1,1,1,2-tetrafluoroethane in a motor vehicle air-conditioning unit witha heat-transfer fluid, in which the heat-transfer fluid is combined witha lubricant oil to form a heat-transfer composition, said heat-transfercomposition comprising the heat transfer fluid and polyalkylene glycol,wherein the heat transfer fluid comprises: 55-85% of2,3,3,3-tetrafluoropropene; and 15-45% of 1,1,1,2-tetrafluoroethane,wherein the polyalkylene glycol has a viscosity from 20 to 100 Cst at40° C.
 2. The method as claimed in claim 1, wherein2,3,3,3-tetrafluoropropene, 1,1,1,2-tetrafluoroethane and polyalkyleneglycol represent at least 95% of the heat-transfer composition.
 3. Themethod as claimed in claim 1, wherein 2,3,3,3-tetrafluoropropene,1,1,1,2-tetrafluoroethane and polyalkylene glycol represent at least 99%of the heat-transfer composition.
 4. The method as claimed in claim 1,wherein 2,3,3,3-tetrafluoropropene, 1,1,1,2-tetrafluoroethane andpolyalkylene glycol represent at least 99.9% of the heat-transfercomposition.
 5. The method as claimed in claim 1, wherein theheat-transfer composition comprises from 1% to 99% of polyalkyleneglycol.
 6. The method as claimed in claim 1, wherein the heat-transfercomposition comprises from 5% to 50% of polyalkylene glycol.
 7. Themethod as claimed in claim 1, wherein the heat-transfer compositioncomprises from 10% to 40% of polyalkylene glycol.
 8. The method asclaimed in claim 1, wherein the heat-transfer composition comprises from15% to 35% of polyalkylene glycol.
 9. The method as claimed in claim 1,wherein the polyalkylene glycol has a viscosity from 40 to 50centistokes at 40° C.
 10. The method as claimed in claim 1, wherein theheat-transfer composition further comprises one or more additives chosenfrom heat-transfer compounds, lubricants, stabilizers, surfactants,tracers, fluorescers, odorant agents, solubilizers, and mixturesthereof.
 11. The method as claimed in claim 1, wherein the heat-transfercomposition further comprises one or more additives chosen fromstabilizers, surfactants, tracers, fluorescers, odorant agents andsolubilizers, and mixtures thereof.
 12. The method as claimed in claim1, wherein the heat-transfer composition consists of2,3,3,3-tetrafluoropropene, 1,1,1,2-tetrafluoroethane, polyalkyleneglycol, and optionally one or more additives chosen from stabilizers,surfactants, tracers, fluorescers, odorant agents and solubilizers, andmixtures thereof.
 13. A method comprising replacing1,1,1,2-tetrafluoroethane in a motor vehicle air-conditioning unit witha heat-transfer fluid, in which the heat-transfer fluid is combined witha lubricant oil to form a heat-transfer composition, said heat-transfercomposition comprising 2,3,3,3-tetrafluoropropene,1,1,1,2-tetrafluoroethane and polyalkylene glycol, wherein thepolyalkylene glycol has a viscosity from 20 to 100 Cst at 40° C.